1. Field of the Invention
The present invention relates to a boundary detector and a boundary detecting method that acquire image information based on an image supplied from a camera that is mounted on a vehicle and that picks up an image of a road surface, and detect a boundary drawn on the road surface based on the acquired image information.
2. Description of the Related Art
In recent years, an apparatus has been developed for picking up an image of a road surface in front of a vehicle with a camera, detecting a boundary, i.e., a white line, drawn on the road surface based on the image picked up by the camera, and automatically driving the vehicle on a lane delineated by the white line. For the realization of automatic driving, the lane must be properly detected, in other words, a detector is required for processing the image picked up by the camera to detect the lane, i.e., the white lines. Such detectors are disclosed in Japanese Patent Applications Laid-Open Nos. H08-320997, and 2001-014595, for example.
A vehicle lane detector disclosed in Japanese Patent Application Laid-Open No. H08-320997, measures a maximum value of edge point counts of an edge component that represents a straight line component, based on image information on the right and the left sides of the vehicle and immediately in front of the vehicle. The vehicle lane detector, based on the measured maximum value, recognizes that the image belongs to a dotted lane marker when the maximum value changes periodically, and that the image belongs to a solid lane marker when the maximum value remains constant. Thus, the vehicle lane detector recognizes the lane of the vehicle based on the results of recognition of the right and the left lane markers.
Another vehicle lane detector disclosed in Japanese Patent Application Laid-Open No. 2001-014595, detects white line candidate points through processing of an image captured by a video camera attached to a front part of a vehicle. The vehicle lane detector selects only the white line candidate points that are determined to be a part of a white line among all the white line candidate points, to calculate a detection ratio, and determines a type of the white line based on the detection ratio.
On an express highway, for example, a plurality of main lanes is provided together with a branch lane to guide the vehicle into a service area, an exit, or the like. The branch lanes form a V-shaped branch with the main lane and a white line for the branch is drawn so as to bend outward from the white line of the main lane. When a vehicle is running on the main lane and encounters a leftward branch, a white line detector mounted on the vehicle may mistakenly detect the white line of the branch lane as the white line of the main lane. Hence the detector must be capable of correctly distinguishing the white line of the main lane from the white line of the branch lane. Above described two patent applications do not particularly disclose techniques to prevent such inconvenience and therefore are not immune to detection error of the white lines delineating the lanes.